Despite recent progress toward sexual equality, it's still a man's world in many ways. But numerous studies show that when it come...

2013年2月21日星期四

Interesting research-Why tongue twisters are so hard to say?

A research published in the journal Nature has shed light on exactly why tongue-twisters like 'she sells sea shells
on the sea shore' are so hard to say.

It found the brain exercises split-second,
symphony-like control to coordinate the tongue, jaw, tongue and larynx to
articulate the words we speak.

In the same way an orchestra relies on a
conductor to coordinate the orchestra's plucks, beats or blows to make music,
speaking demands well-timed instructions from the brain to orchestrate these
various parts.

So, like a conductor's gestures being
picked up by the wrong player, when the brain sends messages to muscles near
each other that make different sounds, confusion can ensue.

The research by a team from the University
of California, San Francisco has potentially important implications for the
treatment of speech disorders.

It also sheds light on an ability that is
unique to humans among living creatures but poorly understood.

'Speaking is so fundamental to who we are
as humans – nearly all of us learn to speak,' said senior author Edward Chang,
a neurosurgeon at UCSF.

'It's probably the most complex motor
activity we do.'

The complexity comes from the fact that
spoken words require the coordinated efforts of numerous 'articulators' in the
vocal tract – the lips, tongue, jaw and larynx.

However, until now, scientists have not
understood how the movements of these distinct articulators are precisely
coordinated in the brain.

To shed light on how speech articulation
works, Dr Chang and his colleagues recorded electrical activity directly from
the brains of three people undergoing brain surgery at UCSF.

By implanting an electrode array under the
skull of the outer surface of the patients' brains, they were able to record
neural activity related to the enunciation of various commonly-spoken English
syllables.

They used this information to determine the
spatial organisation of the 'speech sensorimotor cortex,' which controls the
lips, tongue, jaw, larynx as a person speaks.

This gave them a map of which parts of the
brain control which parts of the vocal tract.

They then applied a sophisticated new
method called 'state-space' analysis to observe the complex spatial and
temporal patterns of neural activity in the speech sensorimotor cortex that
play out as someone speaks.

This revealed a surprising sophistication
in how the brain's speech sensorimotor cortex works.

They found that this cortical area has a
hierarchical and cyclical structure that exerts a split-second, symphony-like
control over the tongue, jaw, larynx and lips.

For example, the neural patterns involved
in pronouncing consonants, they found, were quite different from those for
vowels, even where they used exactly the same parts of the vocal tract, Dr
Chang told Nature.com.

That difference could help to explain why
slips of the tongue happen in predictable ways. In so-called spoonerisms, we
often mix up two consonants, or two vowels, but hardly ever do people
mistakenly swap consonants for vowels.

Findings also showed the brain seems to
coordinate its articulation of words not by what they sound like, as was
previously believed, but by which muscles it needs to move.

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